Formation of polycrystalline SiGe thin films by the RF magnetron sputtering method with Ar-H2 mixture gases

Polycrystalline silicon-germanium (SiGe) films were prepared on corning ?7059 substrates by an RF magnetron sputtering method. The crystallization temperature of SiGe films could be decreased from 600 to 400 °C due to the introduction of H₂ into the sputtering gases probably because of the enhancement of the surface reaction caused by the hydrogen radicals. The optical absorption coefficients of SiGe films by the Ar-H₂ gas sputtering are similar to those of the single crystalline SiGe, nevertheless much higher values are observed in SiGe films by the Ar sputtering. The dark conductivity of the films decreases from 1.2×10⁻² to 2.1×10⁻⁶ S/cm, and their properties seem closer to the intrinsic properties with the introduction of H₂. These results suggest that the introduction of H₂ into the sputtering gases is effective to decrease the crystallization temperature and to improve the optical and electrical properties of SiGe films.     

Effect of Pt/alumina catalyst preparation method on sensing performance of thermoelectric hydrogen sensor

We fabricated three different Pt/alumina catalysts for micro-thermoelectric hydrogen sensor (micro-THS). In the three Pt/alumina catalysts, two were prepared by impregnation of a commercial alumina with an aqueous solution of platinum (IV) chloride pentahydrate, and the third was prepared by impregnation of commercial alumina and nano-Pt with isobornyl acetate solution. To fabricate the micro-THS, the three Pt/alumina catalysts were integrated on thin membrane of the micro-THS, and its hydrogen sensing properties were investigated. The micro-THS with nano-Pt loaded alumina catalyst showed better sensing performance than those with Pt/alumina catalysts prepared by an aqueous solution of platinum (IV) chloride pentahydrate, because of effectively dispersed nano-Pt metal grain on the surface alumina grain observed by TEM. Its voltage signal was 15.7 mV for hydrogen concentration of 1% in dry air at catalyst temperature of 100°C.     

High coercivity of ordered macroporous FePt films synthesized via colloidal templates

The preparation of a three-dimensionally (3D) ordered macroporous iron-platinum (FePt) film derived from monodisperse FePt nanoparticles (approximately 3 nm in diameter) and polystyrene latex particles (254 nm in diameter) is described. The prepared film has a hexagonally ordered porous structure and coercivity up to 10 kOe after annealing at a temperature of 600 degrees C. We also found that size of FePt particles was maintained at around 3 nm, even after annealing at a temperature of 600 degrees C.     

Transient Spectroscopy of Optical Spin Injection in ZnMnSe/ZnCdSe Quantum Structures

We show, by time-resolved magneto-photoluminescence (PL) spectroscopy in combination with selective laser excitation, that optical polarization of the ZnCdSe spin detector induced by spin injection from the ZnMnSe spin injector persists over a much longer time scale than the lifetime of the ZnMnSe excitons. This finding provides compelling experimental evidence that the dominant mechanism for the observed spin injection in the ZnMnSe/ZnCdSe structures should not be due to injection of the excitonic spins of the diluted magnetic semiconductor (DMS). It is rather due to e.g. a delayed spin injection arising from tunneling of individual carriers or/and trapped spins in ZnMnSe.     

Giant Zeeman Effects and Spin Dynamics of Excitons in Dense Self-Organized Quantum Dots of CdSe and Cd1?xMnxSe

Giant Zeeman effects and spin dynamics of excitons are studied in dense self-organized quantum dots (QDs) of CdSe and Cd_1–xMn_xSe. Microphotoluminescence (PL) measurements for each individual dot reveal the typical dot diameter of 3.5 ± 0.2 nm and the density of 5000 m^–2 in the CdSe QDs. The exciton lifetime is shorter in smaller dots with higher energies, indicating energy transfer and tunneling processes among the dots. Circular polarization of excitonic PL is observed at 0 T with an opposite sign to that of the excited light and with the rise time of 50 ps. The CdSe QDs coupled with a Zn_1–xMn_xSe layer show the giant Zeeman shift of exciton, arising from overlapping of exciton wavefunctions in the dots with Mn ions. Spin polarization dynamics in the coupled QDs is also studied.     

Giant Magneto-Optical Properties in Hybrid Nanostructures of Diluted Magnetic Semiconductors With Ferromagnetic Co Wires

Giant Zeeman effects of excitons were studied in hybrid nanostructures of diluted magnetic semiconductor (DMS) quantum wells (QWs) with ferromagnetic Co, where the DMS-QW wires with the width of 200 nm were sandwiched in the Co wires with the width of 400 nm. When the direction of the Co magnetization is normal to the wire plane, a magnetic field B ^⊥ _Co‐flux perpendicular to the well plane can be applied from the Co wires to all of the DMS-QW wire. In addition, the use of a Co/Pt multilayered film with the perpendicular magnetization at zero external field was examined instead of the pure Co film. The excitonic photoluminescence spectrum from the DMS-QW shows significant broadening in the hybrid structures, indicating the giant Zeeman shift of excitons induced by B ^⊥ _Co‐flux.     

Pump–Probe Spectroscopy of Exciton Spin Injection Process in Diluted Magnetic Quantum Wells

Ultrafast spin dynamics of excitons is studied in a double quantum well composed of Cd_0.92Mn_0.08Te and CdTe wells with a Cd_0.80Mg_0.20Te tunnel barrier, in magnetic fields, by pump-and-probe absorption spectroscopy. The excitonic injection process is clarified with the injection time of 30 ps from the Cd_0.92Mn_0.08Te spin aligner to the CdTe spin detector. The time dependencies of circularly polarized differential absorbances show directly the spin injection into the CdTe well. The spin relaxation of the injected excitons is observed as a function of energy in the exciton band of the CdTe well. In addition, ultrafast relaxation processes of spin-polarized carriers in the Cd_0.78Mn_0.05Mg_0.17Te barrier are studied, when it is stacked directly with the CdTe well.     

Performance optimisation of the micro pixel chamber

A thorough performance analysis of large-area μ-PIC detectors has been made. Through systematic simulations and comparison with test results of the two detector versions, μ-PIC1 and μ-PIC3, we have identified that low primary electron collection was responsible for the degradation of measured gas gain of the μ-PIC3 device. The test of a new detector, μ-PIC5, fabricated with a narrower inter-cathode gap and anodes raised above the insulator surface, shows a threefold increase in gas gain reaching 10⁴ in argon 80%–ethane 20% gas mixture, which agrees with simulations. The new detector demonstrates a stable long-term operation at high gains, above 6000 measured during more than 70 h with an X-ray source, with a moderate 6% gain increase due to dielectric polarisation.     

Considerations in the design and sensitivity optimization of the micro tactile sensor

Although miniaturization has been considered the only technology with which to increase sensitivity of tactile sensors, we recently developed the micro tactile sensor (MTS) that performs with high sensitivity without microfabrication. In this study, we examined design and sensitivity optimization of the MTS using theory based upon Mason's equivalent circuit. The touch probe, which is attached to the lead zirconate titanate (PZT) element, was expressed as a purely inductive circuit component. Resonance frequency was calculated as a function of the length of the touch probe, and sensitivity was predicted to be dependent on the length. Furthermore, many kinds of MTS were fabricated with different touch probe lengths, and actual sensitivity was measured as phase shift between nonloaded and loaded conditions. And, from the consideration of theory and experimental data, a sensitivity coefficient was proposed and found to be useful.     

玻璃纤维增强树脂基复合材料弯曲强度时间温度相关性

研究了玻璃纤维增强树脂基复合材料 (GFRP) 层合板弯曲强度高温加速试验的时间温度相关性。在不同的温度和加载速率下进行了三点弯曲试验。通过弯曲强度控制曲线的时间温度移动因子曲线分析了GFRP层合板的弯曲强度时间温度相关性。探讨了低温短时和高温长时的失效机理。通过玻璃纤维拉伸延迟断裂试验,对GFRP层合板的低温短时弯曲强度的时间温度相关性进行了修正。修正后的弯曲强度控制曲线的时间温度移动因子曲线与基体树脂动态杨氏模量的时间温度移动因子曲线非常吻合,表明GFRP层合板的弯曲强度取决于基体树脂的粘弹性性能。